When 20,000 women gathered outside the Union Buildings in Pretoria in 1956 to protest to the South African prime minister JG Strijdom against an extension to the pass laws, they sang: "Strijdom, you have tampered with the women, you have struck a rock." They could have been describing Albertina Sisulu, wife of the ANC leader Walter Sisulu. Albertina, who has died aged 92, was quiet and unassuming, but her strength and resilience over a lifetime of persecution and hardship were extraordinary.

She was born Nontsikelelo Thethiwe in the village of Camama, in rural Transkei. Her happy childhood ended when she was 11 with the death of her father, a miner, probably from the lung disease pneumoconiosis. Her mother was always sickly and Albertina – as she was christened by the missionaries who educated her – looked after her three siblings. Twice she had to drop out of school, so she was two years behind the rest of the class when she graduated from Mariazell, a Catholic mission school, in 1939. She wanted to become a nun, but that would have made it difficult to support her family, so she opted for nursing.

In 1940, Albertina started work at the Johannesburg Non-European Hospital. She nursed with Nelson Mandela's first wife, Evelyn, and Walter Sisulu's sister, Barbie – and then she met Walter. He was instantly smitten and they married in 1944, with Mandela as best man. That year, Albertina was the only woman present at the formation of the African National Congress Youth League.

Albertina had been apolitical but soon she became subsumed in Walter's great passion. After April 1963, when he went underground to head the military wing of the ANC, Umkhonto we Sizwe (Spear of the Nation), she became the breadwinner, supporting from her meagre nurse's salary their three sons, Max, Mlungisi, Zwelakhe, two daughters, Lindiwe and Nonkululeko, adopted children Gerald and Beryl, several nephews and nieces and, later, grandchildren. She insisted that their home in Soweto and its garden be immaculate and that every visitor be fed, no matter how little food there was.

Albertina simply carried on where Walter had left off after he and the rest of the ANC leadership were imprisoned at Robben Island in 1964. The state persecuted Albertina relentlessly. She was repeatedly arrested, sometimes under the Terrorism Act, which allowed detention without trial; sometimes on trumped-up charges. Banning orders meant she could not go to meetings or leave the district. One of the reasons given for her first banning order, in 1964, was that she had attended "a multiracial reception at the British consulate".

Max Sisulu's wife, Elinor, wrote in In Our Lifetime, a 2002 biography of her parents-in-law, that what Albertina found hardest to bear was the persecution of her children. Max was forced into exile aged 17. After repeated detentions and torture, Lindiwe fled to Britain via Swaziland, where she pursued doctoral studies at York University. Zwelakhe, a journalist, was detained, tortured and banned. Each detention caused Albertina dreadful anxiety, particularly after her nephew, Kenneth Sisulu, died in custody.

The brutal suppression of the student uprisings of 1976 recruited thousands for Umkhonto we Sizwe. Albertina organised for them to join training camps in neighbouring states. When the United Democratic Front, effectively the internal wing of the ANC, was launched in 1983, Ma Sisulu, as she was known, was elected one its three national presidents. But by that time, she was back in jail. She spent seven months in solitary confinement before being tried for promoting the ANC at a friend's funeral. She was sentenced to four years, two of which were suspended, but was released pending appeal and immediately resumed her political work. Two years later, she was arrested again and charged with treason. There were massive protests. International opinion had swung against apartheid. The state's case collapsed and she was freed again.

Albertina was regarded by many as the mother of the nation. But so was that other famous wife, Winnie Mandela. Albertina was intermittently horrified by Winnie's behaviour but, mindful of the state's desire to set the two women against each other, and the closeness of their husbands, refused to be drawn into public criticism of her. The murder in 1989 of Dr Abu Baker Asvat changed things.

Baker Asvat had set up a mobile clinic in a poor squatter community, and in the early 1980s Albertina went to work for him as his nurse. One day, he was asked to examine two youths sent to him by Winnie for evidence of sexual assault: she claimed to have rescued them from the clutches of a local cleric. Baker Asvat found no signs of assault, which did not please Winnie. Soon afterwards, he was shot in his surgery. Nothing was ever proved, but Albertina had serious misgivings about the circumstances of Baker Asvat's death. Later, in 1997, when the Truth and Reconciliation Commission investigated claims that Winnie Mandela had ordered his killing, Albertina was called to testify but gave no incriminating evidence.

In 1989, she was finally allowed a passport and went abroad for the first time. In the US, she was feted by George Bush Sr and in Britain met Margaret Thatcher. That October, Walter was released. The couple travelled extensively for the next few years, mostly on business. A second honeymoon was taken in a Black Sea dacha after an official visit to the Kremlin. After the first democratic elections in 1994, Albertina became an MP, her power base in women's organisations such as the ANC Women's League and the Federation of South African Women. The plight of women and children was her abiding concern.

Walter died in 2003; at his funeral, a poem written by Albertina, Walter, What Will I Do Without You?, was read out. After his death, she lived quietly in the family home in Linden, a Johannesburg suburb, but her children continue to play a prominent role in South African public life: Lindiwe is minister of defence and Max is speaker of the National Assembly.

Albertina is survived by her children, 26 grandchildren and three great-grandchildren.